Research On Evaluation Indexes For Selection Of Shale Gas Industrial Construction Areas In Southern Sichuan Basin Areas

This paper takes the Longmaxi shale in the Weiyuan block in the southern Sichuan Basin areas as an example,and combines X-ray diffraction,rock organic carbon,reservoir physical properties,and logging interpretation to evaluate the exploration and development benefits of shale gas in the Weiyuan block.Combined with the actual gas production effect,the relevant mathematical analysis methods are used to explore the main geological factors which affect shale gas production capacity,determining the main evaluation indicators of shale gas industrial production areas,and discuss the lower limits of the corresponding evaluation indicators.The research shows that the thickness of the target layer in the Weiyuan block is 37.7?45.7m,the buried depth is1505.7?3709.0m,the TOC content is 2.35%?4.6%,R_o is 1.8%?2.7%,and the gas content is 2.4?7.3m³/t,The effective porosity is 2.0%?11.8%,the brittle mineral index is 61.0%?78.1%,so the Longmaxi shale in the Weiyuan block is a typical favorable area for shale gas exploration and development,but the actual production effect is quite different.Through the Pearson linear correlation analysis method and gray correlation analysis method,we learned that different geological factors have a certain impact on shale gas productivity,and five geological factors:the drilling rate of layer Long₁¹,TOC,effective porosity,brittleness index and the gas content can be used as the important evaluation index to evaluate the shale gas industrial production areas.To meet the lower limit standard of industrial oil flow of 8.0×10⁴m³/d,the drilling rate of layer Long₁¹should not be less than 65%,the lower limit of TOC is 3.3%,and the lower limit of effective porosity is 3.5%.An analysis of the abnormalities in gas content and test output revealed that test output is not necessarily related to total gas content,but is closely related to free gas content and free gas proportion.In order to achieve industrial development,the total gas content should preferably reach 3.0m³/t,and the proportion of free gas should be more than 60%,that is,the free gas content should be at least reach 2.0m³/t.According to the actual application on site,it is found that the improved rock mine brittleness index(BI_bm)can better identify the shale fracturable interval and the fracturing barrier interval,so it is recommended to use BI_bm as the evaluation index of shale reservoir fracturability,and 0.5 as its lower limit standard.